Problems arise when radio receivers, typically car radios, are installed in a confined region where ventilation is difficult or impossible; in car radios, especially, the limited space availability, and thus small size of the receiver and the maximum housing temperature limit the tolerance to heating, and inhibit heat dissipation. The power output available from such receivers thus also is limited. Various circuits are known to improve the efficiency of power output circuits so that heat losses are reduced. Additionally, protective circuits have been proposed which, when a predetermined temperature is reached, either of heat sinks or electronic equipment connected thereto, interrupt the signal path, to permit the equipment which is overheating to cool. After the cooling temperature has been reached, the signal path is again established. This arrangement has the disadvantage that the user of the car radio cannot listen to the program during the cooling period; if the program happens to be an announcement, or, for example, a traffic report, news, or a weather forecast, such an interruption can be particularly annoying.